ABSTRACT: Mississippian Evaporites: A Tool for the Prediction of Paleostructural and Depositional Trends in Mission Canyon and Ratcliffe Reservoirs, U.S. Williston Basin

Michael L. Hendricks

Evaporites exhibit significant changes in strike and depositional thickness when compared to known and inferred geologic structures in the U.S. portion of the Williston basin. The anhydrite edges of various Mission Canyon and Ratcliffe members (Mississippian) commonly follow linear trends that change strike abruptly. In some portions of the basin, this depositional pattern produced anhydrite traps with significant oil accumulations. It is inferred that most of the linearity and strike changes of anhydrite edges are related to Precambrian basement fracture systems which controlled bathymetric gradients and, consequently, basinward progradation of gypsum (anhydrite shoreline trends). By mapping anhydrite depositional edges (zero edges), Mississippian basin configurations ca be related to known and inferred paleostructures.

Mississippian basin-centered and basin-margin salts can also be used to delineate paleostructural trends. In the central basin and along the east flank of the Williston basin, changes in the thickness of certain Charles salts are directly related to known paleostructures and productive trends. Salt isopach data can therefore be used to significantly increase exploration and exploitation success in Mission Canyon and Ratcliffe beds. Along the western flank of the basin, the dissolution edges of Charles salts also delineate paleostructural trends.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990